My Lisp binding for Gtk+ is published to repo.or.cz. You are welcome to browse should you have any interest in it.
I consider the quality of the code to be still below the alpha quality. To use it, you need to create ASDF symlinks to gtk/gtk.asd, glib/glib.asd, gdk/gdk.asd. I've developed and tested it on SBCL AMD64, so other configurations may exhibit various bugs. Deoms are also included and are in the gtk-demo package (location in gtk/gtk.demo.lisp).